This invention relates to improved fluidized-bed electrodes, especially air-depolarized cathodes, and to related apparatus and methods.
One serious limitation of the fluidized-bed electrodes disclosed heretofore is that the upward flow of the supporting electrolyte through the bed can not exceed a certain optimum value beyond which the current-carrying capacity of the electrode decreases. This optimum flow corresponds to rather low bed expansions, usually about 10% or less. Higher bed expansions result in reduced interparticle contacts, and hence in reduced charge transfer. To maintain the expansion sufficiently low and yet permit the electrolyte flow rate to be sufficiently high for adequate mass transport, the specific gravity of the fluidized particles should preferably exceed that of the supporting electrolyte by at least 2 gm/cm.sup.3. This limitation would preclude the use of activated carbon and of other relatively light materials in fluidized-bed electrodes. Yet activated carbon has several most desirable features, including a high active surface area per unit weight, a high catalytic activity, and low cost, which make it an especially outstanding candidate material for the fluidized particles in air cathodes.
It is an object of my invention to overcome the afore-outlined limitations of present fluidized-bed electrodes, and thereby increase their current-carrying capacity. It is also an object of my invention to permit the use of activated carbon as the chief component of the fluidized particles in fluidized-bed electrodes, especially air-depolarized cathodes.